chore(spec): advance the authorable-surface deletion-gate anchor to main's tip

`gen:authorable-surface-base` re-anchors the committed baseline on this branch's
own merge base with origin/main. The deletion gate compares against the baseline
at that merge base, which a commit inside a feature PR cannot rewrite — so the
advance only takes effect once it is on `main`, which is why it lands here on its
own rather than inside the PR that needs it.

Anchor: 53ef057 (7836 keys) -> 85c6d76 (7804 keys). Generated output
only; no schema, no root set and no other file is touched.

Claude-Session: https://claude.ai/code/session_01KB5PFtxuy1x3dcR5gxudx6
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude